Onigumo was a bandit who got his big break when the priestess Kikyou found him and nursed him back to health. But instead of turning over a new leaf, he basically fed himself to a bunch of youkai, which is exactly as dark as it sounds. This whole mess is what eventually led to him becoming Naraku—so yeah, he didn't stay reformed for long.
Content compiled by AnimeList.moe from publicly available sources.
